The present invention relates to a workholder apparatus for rigidly clamping a workpiece for machining, and in particular to an apparatus capable of securely supporting workpieces of varying size that is suitable for numerically controlled machining applications.
When raw material, or partially fabricated components, are to be machined, the workpiece must be securely clamped to a base plate or some other manufacturing platform to hold the workpiece stable at a precise, predictable position in a manner capable of resisting the forces on the workpiece produced by the machining operation to be performed. Typical machining operations include drilling, boring, honing, grinding and milling. In numerically controlled (NC) machining, for example, a machine tool such as a milling head is programmed to follow a very precise path. The workpiece must be located extremely precisely relative to the NC machine datum points/planes from which the machining path is related or measured.
A number of different indexing and clamping systems have been developed to permit a workpiece to be positioned at a specific location on a support plate. Frequently, the clamping means have fingers, jaws, straps or other means that extend over the side of the workpiece opposite the supporting surface. While generally effective, the upper surface clamps must be carefully positioned to avoid interference with the movement of the machine tool, such as a milling head, across the workpiece. The upper surface clamping means also restrict the machine tool""s access to a portion of the workpiece.
Insufficient clamping pressure, or the use of too few clamps, may allow the workpiece to shift during machining, resulting in wasted, out-of-tolerance products and potential damage to the machine tool. Too much clamping pressure may result in damage to the workpiece either directly, or by elastically deforming the workpiece resulting in out-or-tolerance machining operations. Further, errors in clamp placement may result in the machine tool cutter running against the tool, resulting in damage to the clamps and to the machine tool. Such mishap could also result in a safety hazard to nearby personnel.
Another common practice is to use a vise to secure a workpiece when performing various manufacturing and machining operation on the workpiece. Prior art vises are typically used on precision machining equipment, such as numeric controlled equipment, to hold a workpiece during a defined machining operation. Such vises typically employ a pair of moving jaws perhaps with a fixed center jaw to permit simultaneous holding of two workpieces to permit a single working station to simultaneously perform machining operations on two different workpieces. These prior art vises typically use a threaded actuator shaft which has forward threads engaging one moving jaw and reverse threads engaging the other moving jaws to effect simultaneous opposed movement of the two moving jaws toward each other. Alternatively, one of the jaws may be connected in a non-threaded manner to the actuator shaft thereby engaging the workpiece only after the moving jaw has moved the workpiece to the fixed jaw. Prior art vises generally possess minimum flexibility with respect to their adaptability to various types of desired machining operations. In particular, prior art vises squeeze the workpiece between two, generally parallel jaws, relying on the frictional forces between the jaw face and the workpiece to hold the workpiece in place securely. This squeezing action can cause significant and undesirable compressive stresses in the workpiece.
In many workpiece operations, it is desirable to use a workholder that is equipped with jaws and a work surface that are at least as wide as the workpiece being machined to insure that the workpiece is adequately supported during the machining operation. Moreover, with increasing use of numerically controlled machines the workpiece must be clamped to the work platform at a very precise, or indexed, location so that the preprogrammed machining process will produce the desired operations. It is frequently desirable to present multiple workpieces to the machining apparatus, and to be able to machine all surfaces of the workpiece in a single operation, in order to reduce the amount of machine set-up and tool-change time. However, because the width of the work surface and the jaws of prior art workholding vises cannot be expanded to accommodate wider workpieces or pluralities of workpieces, the user may be forced to inventory a number of various sized workholders. Such workholders may typically cost several hundred dollars and, thus, the average machine owner cannot afford to maintain an extensive inventory of such workholder devices. It may also be beneficial to be able to remove a workpiece from the clamping apparatus for inspection or other purposes, and then return it to precisely the same position on the workholder.
There is a continuing need for improved indexing and clamping systems for workpieces to be machined. In particular, there is a need for a system that will reliably hold a workpiece, without slippage, in a manner that leaves most of the workpiece surface accessible for machining operations.
Accordingly, it is an object of the present invention to provide a workholder apparatus for securely and removably holding workpieces for machining operations. The workpieces to be used with the workholding apparatus described herein are pre-fabricated with wedge-shaped grooves along two opposite sides and circular indexing apertures in the bottom surface. The workholder apparatus consists of a main body having a generally flat work surface that includes at least two parallel cylindrical apertures that intersect the mounting surface thereby defining open slots in the work surface. Precisely located index pin apertures are provided in the main body that extend from the work surface into the main body. Index pins are inserted into the index pin apertures with a portion of the index pin protruding upwardly from the work surface. The protruding portion of the index pin slidably engage the indexing apertures on the bottom surface of the workpiece, thereby precisely locating, or indexing, the workpiece on the work surface. Clamp assemblies consisting of a threaded clamp rod with two clamp dogs having a wedge-shaped portion that may be moved toward each other are inserted into the cylindrical apertures of the main body, with the wedge-shaped portion of the clamp dogs protruding above the work surface. The wedge-shaped portion of the clamp dogs engage the wedge-shaped grooves in the workpiece to secure the workpiece to the workholder.
It is a further object of the present invention to provide a workholder apparatus that securely clamps a workpiece for machining operations while introducing minimal compressive stresses in the workpiece.
It is a further object of the present invention to provide a workholder that does not introduce bending stresses into the workpiece.
It is a further object of the present invention to provide a workholder apparatus that can precisely locate the workpiece on the workholder in a repeatable manner so that a workpiece that has been removed from the workholder may be re-installed on the workholder in its original location.
It is a further object of the present invention to provide a workholder apparatus that is modular and extensible to accommodate multiple workpieces and/or workpieces of differing sizes and shapes.
These and such other objects of the invention as will become evident from the disclosure below are met by the invention disclosed herein. In addition to the explicitly claimed method and apparatus described herein, as such, it is to be understood that all new and useful devices or components described herein are considered to constitute a part of the invention, claimable in their own right, whether such is stated with particularity herein or not.